The present invention is generally concerned with mobile radiocommunication systems.
The present invention is in particular applicable to third generation mobile radiocommunication systems, such as in particular UMTS (Universal Mobile Telecommunication System).
In a general way, mobile radiocommunication systems are subject to standardisation; therefore, for more information on such systems, it is possible to refer to the corresponding standards, published by the corresponding standardisation bodies, such as for example 3GPP (<<3rd Generation Partnership Project>>).
The general architecture of a mobile radiocommunication system such as in particular a system of UMTS type is recalled in FIG. 1. The system comprises a mobile radiocommunication network communicating with mobile terminals or UE (<<User Equipement>>) and with external networks (not specifically illustrated).
The mobile radiocommunication network comprises:                a Radio Access Network, or UTRAN (<<UMTS Terrestrial Radio Access Network>>),        a Core Network, or CN.        
Third generation systems, in particular of UMTS type, use a radio access technology of W-CDMA type (where W-CDMA stands for <<Wideband—Code Division Multiple Access>>).
The UTRAN comprises base stations called <<Node B>>, and base station controllers called RNC (<<Radio Network Controller>>). The UTRAN is in relation, on the one hand with mobile terminals UE, via an interface called <<Uu interface>> (or radio interface), and on the other hand with the CN via an interface called <<Iu interface>>. Within the UTRAN, the Nodes B communicate with the RNCs via an interface called <<Iub interface>> and an interface called <<Iur interface>> may also be provided between RNCs.
Power control techniques are generally used in such systems, in particular in systems using a radio access technology of CDMA or W-CDMA type, to improve performances (in terms of quality of service, of capacity, . . . etc.). Such power control techniques in particular include closed-loop power control algorithms, which in turn include inner-loop algorithms and outer-loop algorithms.
The principle of the closed-loop power control algorithm is now recalled, for the downlink for example. In the inner-loop algorithm, the UE periodically estimates the SIR of the signal received from the Node B, and compares this estimated SIR to a target SIR (SIRtarget). If the estimated SIR is lower than the target SIR, the UE sends a command to the Node B for the Node B to increase its transmit power. Otherwise, the UE sends a command to the Node B for the Node B to decrease its transmit power. The target SIR is chosen by the UE as a function of the required quality of service, according to the outer-loop algorithm.
For example, for systems such as UMTS, such a closed-loop power control algorithm is specified in Technical Specification 3GPP TS 25.214.
Further, in the 3GPP standard (release R99 and later releases), an algorithm, known as ‘limited power raise algorithm’ has been specified, see in particular section 5.2.1.2.2 of TS 25.214 V5.6.0 (2003-09).
The aim of this algorithm is to avoid increasing too rapidly the Node B transmit power. Indeed, in case of deep fading hole, it is preferable to not increase the power too much, since in any case, the power increase will not be fast enough to avoid loosing some data, and since this power increase would cost a significant power resources (that could not be used by other UEs).
In summary, the limited power raise algorithm as currently specified in the standard is the following:
A power control command requiring a power increase, or UP power control command, or UP TPC (where TPC stands for Transmit Power Control), is not applied if the transmit power would be increased by more than Power13 Raise13 Limit dB over the last DL13 Power13 Averaging13 Window13 Size TPC commands.
Power13 Raise13 Limit and DL13 Power13 Averaging13 Window13 Size are parameters of the algorithm and are configured in the Node B by the RNC, using the NBAP (Node B Application Part) protocol at the cell setup (message ‘cell setup request’ sent by the RNC to the Node B).
The limited power raise algorithm is implemented in the Node B.
The downlink power control algorithm as currently specified in the 3GPP standard is more particularly as follows.
Upon receiving a TPC command, UTRAN shall adjust its downlink DPCCH/DPDCH (Dedicated Physical Control Channel/Dedicated Physical Data Channel) power accordingly. UTRAN shall estimate the transmitted TPC command TPCest to be 0 or 1, and shall update the power.
After estimating the k:th TPC command, UTRAN shall adjust the current downlink power P(k−1) [dB] to a new power P(k) [dB] according to the following formula:P(k)=P(k−1)+PTPC(k)+Pbal(k),
where PTPC(k) is the k:th power adjustment due to the inner loop power control, and Pbal(k) [dB] is a correction according to the downlink power control procedure for balancing radio link powers towards a common reference power.
PTPC(k) is calculated according to the following:
If the value of Limited Power Increase Used parameter is ‘Not used’, then
                                          P            TPC                    ⁡                      (            k            )                          =                  {                                                                                          +                                          Δ                      TPC                                                                                                                                  if                      ⁢                                                                                          ⁢                                                                        TPC                          est                                                ⁡                                                  (                          k                          )                                                                                      =                    1                                                                                                                    -                                          Δ                      TPC                                                                                                                                  if                      ⁢                                                                                          ⁢                                                                        TPC                          est                                                ⁡                                                  (                          k                          )                                                                                      =                    0                                                                        ,                                          [                dB                ]                            .                                                          (        1        )            
If the value of Limited Power Increase Used parameter is ‘Used’, then the k:th inner loop power adjustment shall be calculated as:
                                          P            TPC                    ⁡                      (            k            )                          =                  {                                                                                          +                                          Δ                      TPC                                                                                                                                  if                      ⁢                                                                                          ⁢                                                                        TPC                          est                                                ⁡                                                  (                          k                          )                                                                                      =                                                                                            1                          ⁢                                                                                                          ⁢                          and                          ⁢                                                                                                          ⁢                                                                                    Δ                              sum                                                        ⁡                                                          (                              k                              )                                                                                                      +                                                  Δ                          TPC                                                                    <                                              Power_Raise                        ⁢                        _Limit                                                                                                                                          0                                                                                            if                      ⁢                                                                                          ⁢                                                                        TPC                          est                                                ⁡                                                  (                          k                          )                                                                                      =                                                                                            1                          ⁢                                                                                                          ⁢                          and                          ⁢                                                                                                          ⁢                                                                                    Δ                              sum                                                        ⁡                                                          (                              k                              )                                                                                                      +                                                  Δ                          TPC                                                                    ≥                                              Power_Raise                        ⁢                        _Limit                                                                                                                                                              -                                          Δ                      TPC                                                                                                                                  if                      ⁢                                                                                          ⁢                                                                        TPC                          est                                                ⁡                                                  (                          k                          )                                                                                      =                    0                                                                        ,                                                            [                  dB                  ]                                ⁢                                                                  ⁢                where                ⁢                                                                  ⁢                                                      Δ                    sum                                    ⁡                                      (                    k                    )                                                              =                                                ∑                                      i                    =                                          k                      -                                              DL_Power                        ⁢                        _Averaging                        ⁢                        _Window                        ⁢                        _Size                                                                                                  k                    -                    1                                                  ⁢                                                      P                    TPC                                    ⁡                                      (                    i                    )                                                                                                          (        2        )            
is the temporary sum of the last DL13 Power13 Averaging13 Window13 Size inner loop power adjustments (in dB).
For the first (DL13 Power13 Averaging13 Window13 Size−1) adjustments after the activation of the limited power increase method, formula (1) shall be used instead of formula (2). Power_Raise_Limit and DL_Power_Averaging13 Window_Size are parameters configured in the UTRAN.
The power control step size ΔTPC can take four values: 0.5, 1, 1.5 or 2 dB. It is mandatory for UTRAN to support ΔTPC of 1 dB, while support of other step sizes is optional.
The average power of transmitted DPDCH (Dedicated Physical Data Channel) symbols over one timeslot shall not exceed Maximum_DL_Power (dB), nor shall it be below Minimum_DL13 Power (dB). Transmitted DPDCH symbol means here a complex QPSK symbol before spreading which does not contain DTX (Discontinuous Transmission). Maximum13 DL_Power (dB) and Minimum_DL_Power (dB) are power limits for one channelisation code, relative to the primary CPICH (Common Pilot Channel) power, as further specified in the 3GPP standard.
Further, in compressed mode, the same algorithm as in normal mode applies but replacing the definition of P(k) by:P(k)=P(k−1)+PTPC(k)+Pbal(k)+Psir(k)                where Psir(k) is the k:th power adjustment due to the downlink target SIR (Signal-to-Interference Ratio) variation in compressed mode        with Psir(k)=δPcurr−δPprev, where δPcurr and δPprev are respectively the value of δP in the current slot and in the most recently transmitted slot, and the expression of δP is given in TS 25.214.        